This invention relates to capacitors in general and more particularly to an improved capacitor for use with stripline circuit layouts.
Striplines are finding wide use in microwave circuits. With such stripline circuits, the circuit designer has basically one parameter to control the impedance and propagation characteristics for the circuit line. Once the dielectric constant and thickness of the mounting board for the striplines are determined and specified and it has been provided with a proper surface finish to minimize discontinuity in the conductor pattern, then, the width of the conductor pattern which makes the stripline controls the electrical characteristics, particularly the characteristic impedance. The line width may be varied depending on the major frequencies which are to be deployed upon it in order to reduce propagation losses for a particular use. The width used may be, for example, 0.050 inches, 0.045 inches, 0.030 inches, 0.025 inches, 0.020 inches and other suitable widths for a particular design.
In many circuits it is necessary to interrupt the stripline and insert a capacitor for d.c. blocking purposes. Such may occur where in the circuit design it is desired to have one side of the circuit at one d.c. potential and another side at another d.c. potential. In many cases blocking must be done to isolate circuit sections to add energy in the form of d.c. potentials. In other cases, it is desired to have capacitive coupling from one line to another, for phase shifting or other methods of coupling. Again, in such cases, one line is connected to the other by means of a capacitor. Bypassing is done in other cases to remove spurious or unwanted signals.
In microwave circuits of this nature, it has not been possible with known devices to insert capacitors either for d.c. blocking purposes or for bypassing or coupling without concomitant loss to the circuit. The capacitors protrude upward from the boards and stripline. In other cases they have sizes different from the striplines or have electrodes which are not parallel to the striplines. Others have weak or inductive connections or other similar problems.
Thus, the need for an improved capacitor structure for use with stripline circuits becomes evident.